Anaplastic thyroid carcinoma (hereinafter referred to as “ATC”) accounts for 2% to 5% of thyroid carcinoma, and it is one type of carcinoma having an extremely high degree of malignancy. Well-differentiated thyroid carcinoma (WDTC), namely, papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma have a good prognosis. In contrast, ATC is considered as a solid cancer having an extremely poor prognosis. The median survival period of ATC is said to be 4 to 12 months. It has been known that ATC shares several genetic abnormalities with WDTC (point mutations of RAS gene and BRAF gene, point mutation or gene amplification of PIK3CA gene, etc.). On the other hand, mutation of a TP53 gene rarely occurs in WDTC, but it has been known that TP53 gene has been mutated in 70% or more of ATC. Based on the histological correlation of ATC with WDTC, it has been considered that ATC develops from WDTC serving as a previous stage. However, several types of ATCs newly develop (de novo ATC). Thus, under the current circumstances, the molecular mechanism of ATC in terms of the degree of malignancy has hardly been clarified.
As a result of recent progress in molecular-targeted therapy for cancer genes, it is considered that detailed clarification of the mutated regions of gene in ATC leads to the development of an effective therapy.
A change in the copy number of a gene, such as amplification or homozygous deletion, becomes a marker useful in identifying cancer genes causing malignant transformation or cancer-suppressing genes.
The present inventors had analyzed various cancer cell lines using a conventional high throughput array CGH method, so that they had accomplished identification of new genes that cause malignant transformation. The inventors had analyzed ATC using MCG Cancer Array800 (Yu et al., Oncogene 26, 1178-1187, 2007) as one type of high throughput array. As a result, they had discovered a DUSP26 gene acting as a novel marker gene. However, clarification of the molecular mechanism of ATC has been still insufficient, and thus further analyses have been desired.